This invention relates generally to combustion and is particularly useful for carrying out combustion with reduced generation of nitrogen oxides.
Nitrogen oxides (NOx) are a significant pollutant generated during combustion and it is desirable to reduce their generation in carrying out combustion. It is known that combustion may be carried out with reduced NOx generation by using technically pure oxygen or oxygen-enriched air as the oxidant as this reduces the amount of nitrogen provided to the combustion reaction on an equivalent oxygen basis. However the use of an oxidant having a higher oxygen concentration causes the combustion reaction to run at a higher temperature and this higher temperature kinetically favors the formation of NOx.
Accordingly, it is an object of this invention to provide a method for carrying out combustion, which may be practiced using an oxidant having a higher oxygen concentration than that of air, while achieving reduced generation of nitrogen oxides.
The above and other objects, which will become apparent to one skilled in the art upon a reading of this disclosure, are attained by the present invention which is:
A method for carrying out combustion while achieving reduced generation of nitrogen oxides comprising:
(A) injecting primary fuel and primary oxidant into a combustion zone in a ratio within the range of from 5 to 50 percent of stoichiometric, said primary oxidant being a fluid having an oxygen concentration of at least 30 volume percent;
(B) injecting secondary oxidant into the combustion zone at a point spaced from where said primary fuel and primary oxidant are injected into the combustion zone;
(C) combusting primary fuel and primary oxidant within the combustion zone separate from the secondary oxidant to produce combustion reaction products; and
(D) mixing secondary oxidant with combustion reaction products within the combustion zone and thereafter combusting secondary oxidant with combustion reaction products.
As used herein the terms xe2x80x9cnitrogen oxidesxe2x80x9d and xe2x80x9cNOxxe2x80x9d mean one or more of nitrous oxide (N2O), nitric oxide (NO), nitrogen trioxide (N2O3), dinitrogen tetroxide (N2O4), nitrogen dioxide (NO2), trinitrogen tetroxide (N3O4) and nitrogen trioxide (NO3).
As used herein the term xe2x80x9cproducts of complete combustionxe2x80x9d means one or more of carbon dioxide and water vapor.
As used herein the term xe2x80x9cproducts of incomplete combustionxe2x80x9d means one or more of carbon monoxide, hydrogen, carbon and partially combusted hydrocarbons.
As used herein the term xe2x80x9cunburned fuelxe2x80x9d means fuel which has undergone no combustion and/or products of incomplete combustion.